The present invention generally relates to methods and systems for generating silicon substrates having highly doped layers, and to the use of such silicon substrates for fabricating photodetectors and photovoltaic devices.
Modern semiconductor circuits are predominantly based on silicon. Silicon is an indirect band-gap semiconductor with a band-gap of about 1.05 eV. Thus, silicon is not particularly suitable for detecting radiation in the infrared portion of the electromagnetic spectrum. It is, however, known that hyperdoping silicon with a suitable dopant (e.g., sulfur) can extend the absorption spectrum of silicon to the infrared portion of the spectrum. U.S. Pat. Nos. 7,057,256, 7,354,792, 7,781,856, 8,080,467, and 8,604,580 (which are herein incorporated by reference in their entirety) disclose methods and systems for generating a hyperdoped layer in a silicon substrate, e.g., a layer with a doping concentration in a range of 0.5-1.5 atomic percent, as well as silicon with light-trapping surface structures (a silicon substrate having a hyperdoped dopant layer is herein referred to as “hyperdoped black silicon”).
Hyperdoped black silicon fabricated with femtosecond laser irradiation has attracted research and commercial interest for infrared photodetectors and intermediate band photovoltaics due to its light-trapping surface and its ability to absorb sub-bandgap radiation. However, hyperdoped black silicon can contain amorphous silicon, among other material phases that may be in some cases undesirable. Thermal annealing can be employed to reduce this amorphous silicon. Thermal annealing may, however, cause a considerable decrease in the sub-bandgap radiation absorptance.
There is still a need for improved methods and systems for generating highly doped silicon substrates, which can be used for fabricating silicon-based photodetectors and photovoltaic devices.